Light and electron microscopic findings in papillary endothelial hyperplasia of the mandible in a 49-year-old female are reported. The endothelial cell-lined papillary projection into a cystic lumen was examined by light microscopy and characteristic features of the endothelial cells were found by electron microscopy. Factor VIII-related antigen was demonstrated in the endothelial cells by the immunoperoxidase technique.

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Expression of brain-associated small-cell lung cancer antigen (BASCA) in developing lung and in lung tumors was investigated immunohistochemically and immunoelectron miaoscopically with monodonal antibodies recognizing different epitopes of BASCA. In fetal lung, epithelial and mesenchymal cells had different spatial and temporal expression l tterns, in contrast to the consistent ttem in neural cells The cell membranes ofepitheial cells ofthe proximal bronchial tubes were diffusely positive at the pseudoglandular stage. Ciliated cells lost immunoreactivity shortly after their emergence, but non-ciliated cells, induding endocrine cells, lost it at the alveolar stage. The immunoreactivity in mesenchymal cells was reduced in the proximal airway,

A new human epithelial cell line (MK—1) has been established from a well differentiated squamous cell carcinoma of the gingiva. It has been subcultured 90 times during the past 23 months. The population doubling time of the MK—1 cell line was 28 h. A colony forming ability with 18% plating efficiency was shown. Chromosomal analysis revealed an aneuploid human male karyotype with 22 marker chromosomes. The modal chromosome number was 75. Scanning electron micrographs of MK—1 cells showed numerous microvilli and intercellular bridges. Transmission electron micrographs of MK—1 cells showed epithelial characteristics with desmosomes, tonofilaments and membrane‐coating granules. Hetero‐transplantation of cultured MK—1 cells produced tumors, the histology of which was similar to that of original ones. The ultrastructure of the tumors showed the presence of abundant tonofibrils and keratohyalin granules. This MK—1 cell line is a model useful for the study of keratinization of squamous cell carcinomas.

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